Glycol ethers comprise a large class of chemicals with ethylene-based glycol ethers being the most heavily produced. While 2-methoxyethanol (ME) mainly targets the reproductive, developmental, and immune systems, an increase in the length of the alkyl carbon chain decreases such toxicities and increases the hemolytic activity, with 2-butoxyethanol being the most potent. Comparison of the in vitro effects of BAA on blood obtain from various mammals showed that rats, mice, hamsters, rabbits, and baboons were highly sensitive, while pigs, dogs, cats, guinea pigs, and humans were minimally affected. These in vitro findings were confirmed in vivo using guinea pigs and rats. Present studies focused on investigating the effect of species on ME induced testicular toxicity. ME produces testicular lesions characterized by pachytene spermatocyte degeneration in rats and guinea pigs which differ in onset, severity and morphological characteristics. In the rat, degenerating spermatocytes appear necrotic at 24 hrs, while in the guinea pig, they appear apoptotic 96 hrs after the start of dosing. To Further examine if the spermatocyte degeneration in both species represented necrosis or apoptosis, the extent and nature of nuclear DNA fragmentation after ME exposure was assessed both visually using an in situ nucleotide 3' end-labeling (ISEL) procedure and by DNA gel electrophoresis. Testes from rats given a single oral dose of ME (200 mg/kg) showed the expected pachytene spermatocyte degeneration 24 hrs after dosing, with the nuclear chromatin degradation typical of necrosis. In contrast, testes from guinea pigs given daily oral doses of ME (200 mg/kg) showed spermatocyte degeneration at only 96 hrs after the start of dosing, with marked peripheral nuclear chromatin condensation characteristic of apoptosis. Coincident with the appearance of morphologic changes, degenerating spermatocytes in both species contained fragmented DNA as revealed by the ISEL procedure. The pattern of DNA fragmentation on agarose gels in both species consisted of ordered multiples or "ladders" of ~200 base pairs (bp), a hallmark of apoptosis, with their appearance coincident with the time course of morphologic spermatocyte degeneration and ISEL staining. Preliminary data revealed the appearance of divalent metal cation-dependent endonuclease activity at pH 7.0 in ME-treated immature (24-day-old) rat testes that produces a similar pattern of DNA fragmentation, and which appears to be distinct from activity associated with the spontaneous germ cell degeneration observed in testes of this age.